Various mechanisms for adjusting the pitch of rotatable blades (propellers, fan blades, etc.) have been described heretofore. See for example U.S. Pat. Nos. 494,014; 573,977; 810,032; 1,332,475; 1,407,080; 1,491,589; 1,779,050; 1,806,325; 1,869,280; 2,084,655; 2,354,465; 2,394,011; 2,470,517; 2,478,244; 2,711,796; 2,870,848; 2,885,013; 2,939,334; 3,122,207; 3,138,136; 3,518,022; 3,795,463; Canadian 463,179; French 1,177,427; Italy 547,875; and Japan 57-46091.
Although differently shaped blades have been described for use in driving a boat or other vessel through water, the most commonly used type involves a blade having a helically shaped (twisted) configuration.
Heretofore, when flat bottom boats or other boats of shallow draft entered marshy areas choked with vegetation or thick muddy areas covered with but a few inches of water--situations which can readily be encountered in swamps such as exit in southern Louisiana and in other swampy regions--it was very likely that the boats would become mired and bogged down so that they could not move in any direction. Contributing to the problem was the fact that the driving mechanisms for small boats available on the open market rotate in only one direction and are equipped with helically twisted propellers that can readily become entangled in thick vegetation.